The drain valve used in the ceramic toilet water tank in the existing market is usually coupled a button or a sensing window of the water tank cover to form a mechanical type, hydraulic type, sensing type or air control drain valve, the drain valves are needed to connect to the button or the sensing component in other places, such as in the water tank cover, by pushing bars or electric wires or pipes, when assembling, it needs to assemble the button or the sensing component after the drain valve is assembled. Therefore, existing drain valves has some defects: firstly, the drain valve and the button or sensing component need to be assembled separately, the assembly is complicated and inconvenient; secondly, for a sensing type drain valve, the electric wires are exposed out of the structure and located in the water tank, it goes against the water proof performance.
There are proposal that the sensing control portion to open the drain valve is hanging to the ceramic wall of the water tank, a motor is used to drive the chain to lift the flapper up so as to achieve drainage. However, different ceramic water tank have different wall thickness, not all sensing control component can be hung to the wall, so that it is not suitable for all; besides, as different water tanks have different height, the chain needs to be height adjusted, the assembly is complicated; and as the flapper is located at the center of the water tank, the sensing control component needs to be hung at the center, but when the flapper is open, it blocks at the front of the water tank, thus influencing the sensing operation.